# 事件监听

由于Relation Protocol中定义的事件完全继承自[EIP6239](http://eips.ethereum.org/EIPS/eip-6239)，因此我们需要监听所有符合EIP6239规范的事件：

```solidity
/**
 * @title Semantic Soulbound Token
 * Note: the EIP-165 identifier for this interface is 0xfbafb698
 */
interface ISemanticSBT {
    /**
     * @dev This emits when minting a Semantic Soulbound Token.
     * @param tokenId The identifier for the Semantic Soulbound Token.
     * @param rdfStatements The RDF statements for the Semantic Soulbound Token. An RDF statement is the statement made by an RDF triple.
     */
    event CreateRDF (
        uint256 indexed tokenId,
        string rdfStatements
    );
    /**
     * @dev This emits when updating the RDF data of Semantic Soulbound Token. RDF data is a collection of RDF statements that are used to represent information about resources.
     * @param tokenId The identifier for the Semantic Soulbound Token.
     * @param rdfStatements The RDF statements for the semantic soulbound token. An RDF statement is the statement made by an RDF triple.
     */
    event UpdateRDF (
        uint256 indexed tokenId,
        string rdfStatements
    );
    /**
     * @dev This emits when burning or revoking Semantic Soulbound Token.
     * @param tokenId The identifier for the Semantic Soulbound Token.
     * @param rdfStatements The RDF statements for the Semantic Soulbound Token. An RDF statement is the statement made by an RDF triple.
     */
    event RemoveRDF (
        uint256 indexed tokenId,
        string rdfStatements
    );
    /**
     * @dev Returns the RDF statements of the Semantic Soulbound Token. An RDF statement is the statement made by an RDF triple.
     * @param tokenId The identifier for the Semantic Soulbound Token.
     */
    function rdfOf(uint256 tokenId) external view returns (string memory);
}
```

* CreateRDF：当一个包含RDF语义的SBT被创建的时候会发出此事件。
* UpdateRDF：当一个包含RDF语义的SBT被更新的时候会发出此事件。
* RemoveRDF：当一个包含RDF语义的SBT被销毁的时候会发出此事件。

通过监听链上的这些事件，将会得到一条条包含语义的RDF数据（例如：代码块7-1），这些就是包含用户行为数据的数据。

{% code title="代码块：7-1" %}

```
:Soul_0x0109c8ee3151bde7b6b5d9f37e9d2c4bc16930fe p:following :Soul_0x6247123ec0fe0d25feb811e3c4d4a760c1f2e63e .
```

{% endcode %}

## 使用The Graph索引

通过[The Graph](https://thegraph.com/)可以方便的将用户在区块链上产生的行为数据索引出来，具体请参照[The Graph文档](https://thegraph.com/docs/en/developing/creating-a-subgraph/)。

下面是我们监听到Polygon网络上的行为数据，项目地址：

<https://thegraph.com/hosted-service/subgraph/relationlabs/semantic-sbt>

* 通过The Graph提供的playground进行查询

<figure><img src="/files/Y7QW7GbpePqEG9GzZG35" alt=""><figcaption><p>图 7-2 使用playground进行查询</p></figcaption></figure>

* 通过The Graph提供的GraphQL Api进行查询：

eg: 查询最近两条token的信息

{% code overflow="wrap" %}

```shell
curl --location --request POST 'https://api.thegraph.com/subgraphs/name/relationlabs/semantic-sbt' \
--header 'Content-Type: application/json' \
--data-raw '{"query":"{\n  turtles(first: 2) {\n    id\n    owner\n    tokenId\n    turtle\n  }\n}"}'
```

{% endcode %}

查询结果

{% code overflow="wrap" %}

```shell
{"data":{"turtles":[{"id":"33456276423","owner":"0x16ff7821a8d293cd2ea07b650fc69ea9206d0615","tokenId":"1","turtle":":Activity1 p:name \"Activity_2049_1\" . :Activity1 p:level 1 . "},{"id":"33456276425","owner":"0x16ff7821a8d293cd2ea07b650fc69ea9206d0615","tokenId":"2","turtle":":Activity2 p:name \"Activity_2049_2\" . :Activity2 p:level 2 . "}]}}
```

{% endcode %}

## 使用ethers.js索引

[ethers.js](https://github.com/ethers-io/ethers.js)是一个与以太坊及其生态进行交互的JavaScript库。

例如：

```javascript
const ethers = require('ethers')
const rpc = 'https://polygon-mumbai.blockpi.network/v1/rpc/public'
let abi = ['event CreateRDF(uint256 indexed tokenId, string rdfStatements)']
const provider = new ethers.JsonRpcProvider(rpc)
const iface = new ethers.Interface(abi)
const filter = {}

// listen
provider.on(filter, (e) => {
  try {
    let event = iface.parseLog(e)
    console.log(event)
    // parse ...
  } catch (error) {}
})
```


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